The grue is a sinister, lurking presence in the dark places of the earth. Its favorite diet is
adventurers, but its insatiable appetite is tempered by its fear of light. No grue has ever been seen
by the light of day, and few have survived its fearsome jaws to tell the tale.

The creation of intelligent magical weapons is not an exact science and there are occasional failures, as such think of causing a little more stress to your players by "rewarding" them with an insane magical weapon

eg:
Agrophobic, refuses to come out of the scabbard without a strength check to draw it.

Haemaphobic: afraid of blood, fight at a penalty against any blooded creatures but really good against undead, elementals etc

Schizophrenic, not just one mind in your sword, lets have half a dozen minds in there, all different and bound to cause confusion